1. Field of Invention
The present invention relates to the wireless communication field, and more particularly, to a persistent scheduling method and apparatus based on UE semi-grouping and statistically multiplexing.
2. Description of Prior Art
In Long Term Evolution (LTE) system, all services will be carried in packet domain and thus Voice over IP (VoIP) is an important service for operators. The scheduling is critical to improve the VoIP capacity. From current 3rd Generation Partnership Project (3GPP) status on UpLink (UL) Scheduling principles [Reference 1], both persistent and dynamic scheduling modes for VoIP are allowed for LTE uplink.
For LTE system, it will support quite large number (e.g., 400) of active UEs. Then specifically for uplink, it will consume large number of grants to support a large number of VoIP users, which will reduce the downlink (DL) capacity.
With the constraints on dynamic grant method above, to save the downlink (DL) L1 capacity, dynamic scheduling mode isn't preferred for VoIP services. As a sequence, it becomes an issue to leverage the unused HARQ transmission for each HARQ process. In LTE system, low average transmission number will have high spectrum efficiency with adaptive modulation and coding schemes. Thus the average HARQ transmission number will be typically between 1 and 2 to achieve good spectrum efficiency. In other side, the maximum transmission number will be large (such as 4 or 5) for VoIP service and thus the system should at least allocate the resource for the potential retransmissions up to its maximum transmission number. There is no dynamic grant needed in persistent scheduling mode, however, how to sufficiently leverage the resource in HARQ transmission in persistent manner is still an open point.
To improve the resource utilization, there is a proposal from Motorola [Reference 2] to use dynamic grouping scheduling to group a number of VoIP users to share the resources. Different users should use same MCS and same resource units in one group and thus a number of groups can be defined with different MCS and RU (resource unit) number. However, this proposal needs specific bit-map dynamic grant to indicate which VoIP user in the group will use the time/frequency resource. This conflicts with current grant method in 3GPP and this proposal isn't selected in 3GPP now.
There is another proposal from Alcatel-Lucent [Reference 3] to share the HARQ resource with non-VoIP user. The basic idea is to let the dynamic users use the unused HARQ retransmission opportunities for VoIP (due to successfully transmission of the VoIP packet) to transmit other packet service and when there is a collision, the VoIP packet initial transmission is shifted in time domain. But in frequency-domain, the VoIP packet will use the same resource unit and same MCS. With this approach, the time resource for initial transmission isn't persistent and VoIP service and other dynamic packet services share the same frequency resource. This seems also not feasible from current 3GPP status and system design viewpoint in the case that there is different Bandwidth allocated to VoIP services and other burst services.